Johnston, a former chaplain for the Beaverton Police Department, chronicles his experiences in a self-published book, "Sent to Serve...The Chaplains of 9/11."

"When America was attacked on 9/11 many chaplains believed God was calling them to volunteer," Johnston writes in his book.

During Johnston's stay in New York, visited police officers and firefighters and met with the families of fallen officers.

Among his most vivid memories, Johnston recalls visiting a fire station at Ground Zero and talking to a firefighter who lost five colleagues in the attacks. Throughout their two-hour stay, the chaplains were able to go on the roof -- sacred ground for firefighters -- and get a panoramic view of Ground Zero. The chaplains were also successful in talking to the firefighter about the attacks.

In the 84-page book, Johnston also writes about the work of other chaplains and provides history and context about the profession.

"It's not about war stories, though there are some in there," Johnston said of the book. "I want people to understand what a chaplain is all about."

Chaplains provide spiritual and emotional support for public safety employees, he said. The vast majority of chaplains are volunteers and tend to be retired public safety officers.

"We are there for the personnel," Johnston said. "We are cheerleaders for the police department."

Johnston, who was an associate pastor at the Santa Monica Church of the Nazarene when he began as a police chaplain, began volunteering with the Beaverton Police Department in 1994 and became a "fully-funded volunteer" in 2001. He retired from the Sherwood Police Department in December 2010 after serving as a chaplain for two years.

When officers go through a traumatic event, they can receive support from the human resources department. In Johnston's' experience, officers prefer to to go a chaplain because they are part of the force, he said.

"The chaplain is the one he is going to trust," he said.

Chaplains assist officers by going to their homes and talking to family members, offering a prayer, or simply going on a ride-along and listening to the officer.

Throughout Johnston's 26 years as a chaplain, he served on a mostly volunteer basis and hopes his book inspires others to volunteer - even if it's not as a chaplain.

"9/11 brought thousands of us together," Johnston said. "This is a call for people to volunteer in their community."